FR2504228A1 - Dynamically balanced crankshaft and connecting rod - has rotating counterweight and secondary connecting rod for second weight - Google Patents

Abstract

The mass (M1) is caused to reciprocate by the rotation of the crankshaft (OB) which, alone, would give rise to out-of-balance forces or dynamic imbalance. A second connecting rod (B) is hinged (at B) and connected to a second mass (M2) (at e). The mass (M2) may slide in a crosshead but to reduce wear may be connected by a crank (CD) and allowed to assume a slightly oscillatory movement. A counterweight is mounted on a crank (OE) which extends in a direction diametrically opposite the crank (OB). This arrangement equalises the out-of-balance forces.

Description

 The present invention relates to a transmission mechanism of the connecting rod-crank type, provided with a dynamic balancing device.

More particularly, the invention also relates to a cutting machine provided with a cutting block mounted on such a mechanism.

 A crank-crank mechanism can be used to animate a mass, fixed at the free end of the connecting rod, with an oscillating rectilinear motion. In this movement, alternating forces and couples act on the fixed articulation of the crank. These efforts and these alternative couples generate vibrations which obviously adversely affect the operation of the mechanism. Various stabilizers have been designed to suppress these vibrations or, at least, to reduce their importance.

 These forces and variable couples responsible for the vibrations of the crank-crank mechanisms must be particularly well balanced when these mechanisms are incorporated in production machines operating at fast rates, as is the case, for example, cutting machines equipped with Oscillating cutting or perforating blocks for sheet metal, paper, cardboard, films, etc. Indeed, these vibrations, among other disadvantages, limit the practical production rate of the machine compatible with an acceptable noise level, cause accelerated wear of the parts affected by these vibrations and are at the origin of games responsible for poor reproducibility of movements of parts, incompatible with the cutting tolerances required of high precision machines.

 To prevent these vibrations, a first solution is to ensure a stabilization "static" by masses, mounting the crank-crank mechanism on a strong frame and / or on heavy foundations. However, this solution has the disadvantage of requiring the installation of heavy and bulky equipment, without preventing the wear of the bearings and other bodies subjected to varying forces.

 A second solution is to provide stabilization by insulation and damping using springs, rubber blocks or air cushions. Unfortunately this type of stabilization is only effective for a certain speed of rotation of the crank and is therefore not suitable for a mechanism where it is precisely desired to vary this speed, as is the case in particular in the mechanisms intended for support oscillating cutting blocks, adaptable to various cutting or perforating work.

 A third solution, establishing a "dynamic" balancing, involves an flywheel which rotates with the crank around the axis of rotation thereof, to "smooth" the variations of the torque acting on this axis. This means does not solve the problem of balancing alternating forces applied to the axis of rotation.

 Another solution is to balance, as much as possible, all the efforts and / or couples that cause the vibrations. For this purpose it is possible to connect the crank head to one or more other moving masses, arranged so as to cancel or reduce forces and torques acting on the fixed axis of rotation of the crank. This is the "dynamic" balancing adopted in particular in piston engines, in "star" or "V". A simple mechanism of this type comprises two moving masses on two orthogonal axes, these masses being connected by connecting rods to the head of a crank turning around the intersection of the axes. A satisfactory balancing of the pairs at the intersection of the axes is thus obtained.

On the other hand, efforts at this point are not balanced. In addition, the moving masses are most often guided on their axes by bearings.

which are subject to rapid wear, in machinas at high operating rates.

 The object of the present invention is to provide a crank-and-crank transmission mechanism equipped with a balancing device of the latter type, which has none of the disadvantages mentioned above.

 This object is achieved with a transmission mechanism of the type comprising a first connecting rod mounted between a moving mass M1 in trains tion and a crank rotating about a fixed axis of rotation.

According to the invention, it further comprises (1) a second connecting rod mounted between a second mobile mass M2 and the hinge common to the first connecting rod and the crank so that the torques due to masses M and M2 on the axis fixed rotation equilibrium, and (2) a counterweight of mass m mounted on the crank so as to balance the resultant reactions to the forces applied by the masses M1 and M2 on the common joint to the two connecting rods.

In the attached drawing, given only as an example
FIG. 1 is a diagram of a conventional two-wire transmission mechanism,
FIG. 2 is a diagram of a mechanism of the type of FIG. 1, improved by the addition of a dynamic balancing device according to the invention,
FIG. 3 is a partial diagram of a variant of the mechanism of FIG. 2 and
FIG. 4 represents a practical embodiment of the mechanism of FIG. 2.

 The conventional transmission mechanism of FIG. 1 comprises a crank OB of length R1 which rotates about an axis 0. This crank is connected to a mass M1 by a connecting rod AB articulated in B on the crank and in A on mass M1. . This is guided on a rectilinear trajectory of axis Ox, by known means not shown.

If it is assumed that the length of the connecting rod AB is large relative to that of the crank OB, the elongation x of the center of gravity G of the mass M1 when the crank rotates at the angular speed co is:
x = R1sErxt in relation to the center of the race of M1.

The effort F transmitted in B is therefore approximately

It is an alternative effort.

I1 change de sens quatre fois par tour. Les variations périodiques de < et C entraînent des vibrations et des difficultés de régulation de vitesse.The couple in O is worth

It changes direction four times a turn. Periodic variations of <and C cause vibrations and speed control difficulties.

According to a first embodiment of the invention (see FIG. 2) these drawbacks are overcome by adding, to the conventional crank-crank mechanism, a balancing device consisting of
(1) a second connecting rod BC which moves at C a mass M2, on the perpendicular Oy to the axis of oscillation Ox of the mass M1,
(2) a counterweight m placed on the crank OB so that m and B are on both sides of O.

 The mass M2 can be guided on Oy by bearings. However, such a solution involves wear of the parts by friction on these bearings. This disadvantage is avoided by mounting the mass M2 on a crank CD> as illustrated in FIG. 2. By choosing a crank of sufficient length, M2 is defined as a quasi-rectilinear race, without using bearings.

ce qui donne en O un couple C';
C' # F2 x R1 sin < t

sin 2wt
Le couple C sera équilibré si |C| = IC'I soit si
M2 = M1 (1)
Le schéma partiel de la figure 3 correspond à un outre mode de réalisation de l'invention,dans le quel la masse d'équilibrage M2 est remplacée par un volant d'inertie I, qui tourne autour de D et qui est connecté en C à la bielle BC, C se trouvant sur la perpendiculaire Oy à l'axe Ox.Dans ce cas on aura équilibrage des couples en O si

avec ICDI = R3
L'utilisation d'un volant à la place d'une masse M2 (bien que créant des efforts alternés en D) est d'exécution plus simple et permet de choisir la position d'équilibre du mécanisme à l'arrêt, par décalage du centre de gravité par rapport au centre de rotation(grâce à l'adjonction de masselottes réglables).If it is assumed that the length of the rod BC is large compared to that of the crank OB, the force transmitted in B by the rod BC will be

which gives in O a couple C ';
C '# F2 x R1 sin <t

sin 2wt
The pair C will be balanced if | C | = IC'I be so
M2 = M1 (1)
The partial diagram of FIG. 3 corresponds to another embodiment of the invention, in which the balancing mass M2 is replaced by a flywheel I which rotates around D and which is connected at C to the connecting rod BC, C being on the perpendicular Oy to the Ox axis. In this case we will balance the pairs in O if

with ICDI = R3
The use of a flywheel instead of a mass M2 (although creating alternating forces in D) is simpler execution and allows to choose the balance position of the mechanism at a standstill, by shifting the center of gravity relative to the center of rotation (thanks to the addition of adjustable weights).

 Thus, it is possible to obtain the balancing of the torque in O, and thus the suppression of the vibrations due to a periodic torque, by means of a mass M2 with rectilinear or pseudo-rectilinear guidance (by connecting rod, by parallelogram, by guiding "Evans", etc.).

 To eliminate any vibration, it is also necessary to balance the periodic forces on the bearing 0. This object is achieved, in the balancing devices of FIGS. 2 and 3, using a counterweight m mounted on the crank which turn to O.

In FIGS. 2 and 3, F1 and F2 represent the forces due to the masses M1 and M2, respectively. These efforts generate in B on the mani velle reactions -F1 and -z2 such that
2 | F1 | - M1R1 # 2 sinc t
| F2 | = N2R1 X. coswt = M1R1 #. cos Wt, eir M1 = M2, the pair being balanced as we have seen above (see relation (1)).

The composition of these two reactions gives a resultant FR such that IF | ~ N M1R1 # (taking into account the approximations
R above)
It is a rotating force collinear with OB since the pair in O is zero.

It is therefore possible to balance this force FR by means of a counterweight m mounted in E (| OE | = R2) on the crank which rotates in O, so as to
2 ~~ develop a centrifugal force F such that Fc + FR = o
This result is reached when: m R2 = M1R1 (2)
Thus, to the approximations made, one balances efforts and couples in O using
(1) a mass M2 = M1, or equivalent flywheel, exerting in B a force which creates a torque in O such that it balances that due to mass M1 and,
(2) a counterweight m placed at E on the crank mechanism at a distance OE = R2 such that mR2 = M1R1.

 This complete balancing eliminates the vibrations that are generated by efforts and alternative couples.

 FIG. 4 shows a practical embodiment of a blueling-crank transmission mechanism provided with a balancing device according to the invention. This mechanism serves, in a cutting machine, to move a cutter block of photographic films, general reference 1. This cutter block 1 is mounted oscillating on a parallelogram-mounted support (2, 3) whose arms 2 and 3 are respectively articulated on the frame at 4 and 5, and on the block 1 at 6 and 7. Such a support comprises only joints and is therefore not subject to frictional wear which in the long term affects the supports of bearing type, on which slide the parts to guide.

 The transmission mechanism comprises a rod 8 which is articulated at 9 on a part integral with the block 1. The "crank" is constituted by a disc 10 which rotates about an axis 11. One end of the connecting rod 8 is articulated on this disk around an eccentric axis 12. The disk carries a balance weight m counterweight, centered in the plane of the axes 11 and 12.

 A second connecting rod 13 is articulated at one end on the axis 12 and, at the other end, on an axis 14 integral with a disk M2 pivoting about an eccentric axis 16.

 The cutting block 1, of global mass M1, comprises a support 17 which overflows a bracket 18 which guides a knife 19 movable vertically.

This knife cooperates with a counter knife 20 fixed directly on the support 17. The knife 19 is actuated by a connecting rod 21 mounted at one end at 22 on the knife 19 and at the other end on the eccentric axis 12.

 When the disc 10 rotates under the action of a motor (not shown), the rod 21 communicates an oscillating vertical movement to the knife 19, which then cooperates with the counter-knife 20 to cut "in flight" a moving film following the axis of the arrow F, under the action of drive means (not shown). Indeed, thanks to the rod 8, the cutting block 1 "follows" the film during the cut.

 Comparing this embodiment to the diagram of FIG. 2, note that the foot 14 of the connecting rod 13 is shifted to the left of the plane of the axes 11 and 16 corresponding to the axis Oy of FIG. the position on the axis Oy of the connecting rod C of Figure 2, meets particular characteristics of the embodiment of Figure 4.

 The offset allows, firstly, to define an equilibrium position of the mechanism at rest (low position of the disk M2). On the other hand it takes into account the presence of a moving mass of oscillating vertical movement (the knife 19 and the connecting rod 21). Finally, this offset makes it possible to correct the effects of the use of a rod 8 whose ratio of the length to that of the crank (11,12) is a little weak, compared to that taken into account in the calculations developed. upper.

 It is clear that, apart from the adjustments described above, which are in the field of those skilled in the art, the balancing of the forces and torques around the axis 11 operates as described and shown in connection with FIG. 2, where the axis O plays the role of this axis 11.

 Thanks to the balancing device that equips the transmission mechanism according to the invention, it was possible to operate a cutting block of 25 kg at 1200 strokes / minute, on a stroke of an amplitude of 3.5 cm, without vibration and with a moderate noise. Without this balancing device, the rate would have been limited to about 300 or 400 strokes / minute.

 It will also be noted that the balancing obtained does not depend on the speed of rotation of the axis O (FIGS. 2 and 3). We can therefore vary this speed (and therefore the rate of cutting) without altering the liberation of the mechanism.

 In addition, the torque O being zero, the driving power required is limited to the absorption of friction losses. Balancing also reduces bearing wear in 0.

(voir relation (-2)).The balancing device according to the invention is easily adapted to a variation of the radius R1 of the crank OB. Such a variation is useful, for example, when it is necessary to adapt the stroke of a cutting block to a new cutting format. This variation of the radius R1 will not alter the established equilibrium if R1 and R9 are maintained in the report

(see relation (-2)).

 R2 can be adapted to the new value of R1 by mounting the flyweight m and the articulation B on a means such as a mechanism comprising two screws Oye and OB of opposite steps, so that m and B deviate or move closer to the O axis in the desired proportions.

Claims (9)

1 - Transmission mechanism of the type comprising a first connecting rod  mounted between a movable mass M in translation and a crank  rotating about a fixed axis of rotation, characterized in that  further comprises, in combination, (1) a second connecting rod mounted between a second movable piece M and the common hinge  M2  first crank and crank so that couples due to  masses M1 and M2 on the fixed axis of rotation are balanced, and (2) a  mass counterbalance m mounted on the crank so as to balance  the resultant of the reactions to the forces applied by the masses  M and M on the joint joint to the two connecting rods. 2 - Mechanism according to claim 1, characterized in that the  masses M and M are equal and are movable on perpendicular axes  eyelets which concur on the axis of rotation of the crank, the  connecting rods that connect to this crank being of great lengths  relative to the distance R1 that separates their joint joint from  the axis of rotation of the crank. 3 - Mechanism according to claim 1, characterized in that the  mass M2 is a flywheel connected to the second connecting rod by a  movable eccentric joint in the vicinity of an axis which intersects  the axis of the translation of the mass M1 on the axis of  rotation of the crank, in that the inertia I of the steering wheel is connected  at the distance R3, which separates the axis of rotation of the steering wheel of the articu 2  eccentricity, by the relation I = MlR3, and in that the lengths  connecting rods are large compared to the distance R1 which separates their  common articulation of the axis of rotation of the crank. 4 - Mechanism according to any one of claims 2 and 3,  characterized in that the axis of rotation of the crank is folded  between the counterweight and the common articulation of the connecting rods ,. to one  distance R2 such that  R2 x m = R1 X M1 5 - Mechanism according to claim 4, characterized in that  includes means for simultaneously varying the values dc R1  and R2 without changing the value of their report. 6 - Mechanism according to any one of claims 1 and 2,  characterized in that at least one of the masses M1 and M2 is mounted  on an articulated support defining a quasi-rectilinear guidance.  7 - Mechanism according to any one of claims 1 and 2,  characterized in that at least one of the masses M1 and M2 is guided  in its movement by rectilinear bearings.  8 - Cutting machine comprising an oscillating cutting block, characterized  in that the cutting block is mounted as the mass M1 of the mechanism  according to any one of claims 1 to 7.  9 - Cutting machine comprising an oscillating cutting block, characterized  in that the cutting block is mounted as the mass M1 of the mechanism  according to claim 1, in that the cutting block comprises a  movable knife actuated by a third connecting rod connected to the articula  common connection of the first and second connecting rods and that an engine  rotates the fixed axis of rotation of the crank to operate  simultaneously the three connecting rods. 10 - Machine according to claim 9, for cutting a product in  band, characterized in that it includes means for defying  ler the band between the knife and a counter-knife fixed on the block  cutting.